Demulsification characteristics of high water content emulsion under direct current electric field

• Impurities weaken the interaction energy between oil droplets. • Different impurities affect oil droplet aggregation to varying degrees. • Feasibility verification of demulsification of high water content emulsion. • Cations hinder oil droplet migration and reduce the electric field’s demulsification effect. • Effect of operation process on demulsification effect of high water content emulsion. After long-term water injection, most oilfields have entered high or ultra-high water cut stages, with emulsions transitioning from water-in-oil to oil-in-water types. Electro-coalescence technology is widely applied in oil–water separation due to its high efficiency, low cost, and large processing capacity. Excessive water content increases equipment load and leads to operational instability, scaling, and corrosion. To address this, the feasibility of the device’s principle was verified via molecular dynamics simulation, followed by electrostatic demulsification experiments using a custom-built electrostatic coalescence unit. Simulations showed that electric field intensity enhances droplet coalescence and that impurity components influence the effect. Experimentally, increased voltage amplitude led to greater deformation of dispersed phase droplets, accelerating separation and increasing the height of the bottom clear liquid layer. At 50 V, the oil concentration at the bottom decreased from 2909.22 mg/L to 812.16 mg/L, achieving a 72.1 % reduction. The height of the clear layer rose with initial water content. At an oil-to-water volume ratio of 1:7 (87.5 % water), the clear layer reached 15.8 cm, and the oil concentration dropped from 105,625 mg/L to 527.26 mg/L, yielding a removal rate of 99.5 %. However, extremely high water contents slowed further growth of the clear layer, risking voltage instability and short circuits. Inorganic salt ions weakened the demulsification effect. Moreover, the process of sedimentation followed by electro-dehydration showed superior performance and lower energy consumption than the reverse order or electro-dehydration alone.